The rapid development of optical fibers, which permit transmission over longer distances and at higher bandwidths, has revolutionized the telecommunications industry and has played a major role in the advent of the information age. However, there are limitations to the application of optical fibers. Because laying optical fibers in the field can require a large initial investment, it is not cost effective to extend the reach of optical fibers to sparsely populated areas, such as rural regions or other remote, hard-to-reach areas. Moreover, in many scenarios where a business may want to establish point-to-point links among multiple locations, it may not be economically feasible to lay new fibers.
On the other hand, wireless radio communication devices and systems provide high-speed data transmission over an air interface, making it an attractive technology for providing network connections to areas that are not yet reached by fibers or cables. However, currently available wireless technologies for long-range, point-to-point connections encounter many problems, such as limited range and poor signal quality.
Radio frequency (RF) and microwave antennas represent a class of electronic antennas designed to operate on signals in the megahertz to gigahertz frequency ranges. Conventionally these frequency ranges are used by most broadcast radio, television, and wireless communication (cell phones, Wi-Fi, etc.) systems with higher frequencies often employing parabolic antennas.
A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. Conventionally, a parabolic antenna is includes a portion shaped like a dish and is often referred to as a “dish.” Parabolic antennas provide for high directivity of the radio signal because they have very high gain in a single direction. To achieve narrow beam-widths, the parabolic reflector must typically be much larger than the wavelength of the radio waves used, so parabolic antennas are typically used in the high frequency part of the radio spectrum, at UHF and microwave (SHF) frequencies, where the wavelengths are small enough to allow for manageable antenna sizes. Parabolic antennas may be used in point-to-point communications, such as microwave relay links, WAN/LAN links and spacecraft communication antennas.
The operating principle of a parabolic antenna is that a point source of radio waves at the focal point in front of a parabolic reflector of conductive material will be reflected into a collimated plane wave beam along the axis of the reflector. Conversely, an incoming plane wave parallel to the axis will be focused to a point at the focal point.
Conventional radio devices, including radio devices having parabolic reflectors, suffer from a variety of problems, including difficultly in aligning with an appropriate receiver, monitoring and switching between transmitting and receiving functions, avoiding interference (including reflections and spillover from adjacent radios/antennas), and complying with regulatory requirements without negatively impacting function.
Described herein are devices, methods and systems that may address many of the issues identified above.
Also described herein are systems, devices and methods for RF signal filtration, and more particularly to a polarization-preserving RF filter for microwave applications. Radio frequency (RF) and microwave filters represent a class of electronic filters designed to operate on signals in the megahertz to gigahertz frequency ranges. Conventionally these frequency ranges are used by most broadcast radio, television, and wireless communication (cell phones, Wi-Fi, etc.) systems. Accordingly most RF and microwave devices will include some kind of filtering on the signals transmitted or received. Such filters may be used as building blocks for duplexers and diplexers to combine or separate multiple frequency bands.
Conventional RF and microwave filters are often made up of one or more coupled resonators. The unloaded quality (“Q”) factor of the resonators being used will generally set the selectivity of the filter. In the microwave range (1 GHz and higher), cavity filters become more practical in terms of size and increased Q factor than lumped element resonators and filters, although power handling capability may decrease. However, well-constructed cavity filters are capable of high selectivity even under high power loads. The resonators on conventional filters are limited because a higher Q factor and increased performance stability may only be achieved by increasing the internal volume of the filter cavities.
Increasingly microwave RF filters are required to have wide bandwidth and preserve all polarizations. While generating attenuation poles at specific frequencies in the filter response is well known in standard multi-pole filters, the polarization-preserving characteristic is not always fully realized.